MEM: Fix fs.py by specifying the range size rather than end

This patch fixes the currently broken fs.py by specifying the size of
the bridge range rather than the end address. This effectively
subtracts one when determining the address range for the IO bridge
(from IO bus to membus), and thus avoids the overlapping ranges.

configs/example/fs.py

@@ -167,7 +167,7 @@ if options.caches or options.l2cache:
     test_sys.iocache.mem_side = test_sys.membus.port
 else:
     test_sys.iobridge = Bridge(delay='50ns', nack_delay='4ns',
-                               ranges = [AddrRange(0, mem_size)])
+                               ranges = [AddrRange(mem_size)])
     test_sys.iobridge.slave = test_sys.iobus.port
     test_sys.iobridge.master = test_sys.membus.port